:Avian reticuloendotheliosis virus (REV-T) is the most virulent of all retroviruses and rapidly induces an invariably fatal lymphoma. v-Rel is the most oncogenic member of the Rel/NF-KB family of transcription factors. The ReI/NF-KB family regulates the expression of genes involved in proliferation, apoptosis, defense and wound healing responses, and embryogenesis. The ReI/NF-KB complexes bind to DNA recognition motifs as dimers. Transformation by v-Rel is the result of differential regulation of genes normally controlled by the ReI/NF-KB family. In the nuclei of transformed cells, v-Rel exists as homodimers or in heterodimers with c-ReI, NF-KBl, and NF-KB2. Since the appearance of v-Relheterodimers in the nucleus temporally correlates with an increase in the rate of cell proliferation, the association of v-Rel with endogenous ReI/NF-KB family members is likely to play a critical role in its transforming ability. We have isolated point mutants of v-Rel which have lost their ability to associate with specific ReI/NF-KB family members and propose to employ these point mutants to determine which ReI/NF-KB family members enable v-Rel to transform. The overexpression of v-Rel, results in the elevated expression of c-fos and c-jun and in repressed expression of fra-2 in fibroblast cultures and lymphoid cells. c-jun has been shown to be directly transcriptionally upregulated by v-ReI. Co-infection or sequential infection of fibroblast cultures or lymphoid cells with retroviruses expressing v-rel and a transdominant negative mutant of AP-1 activity, supjun-1, resulted in a reduction of the transformation efficiency of v-Rel. These studies did not define the role of individual AP-1 family members. The role of c-Jun, c-fos, and fra-2 in v-Rel-mediated transformation will be examined. We also propose to determine whether v-Rel directly regulates the differential expression of c-fos and fra-2. Recently, we have found that TClO, a member of the Rho family of small GTPases, is upregulated in v-Rel transformed fibroblasts. Since TCIO and other Rho proteins have been implicated in the organization of the actin cytoskeleton, it is possible that the TC1O-mediated signal transduction pathway may be responsible for the cytoskeletal remodeling observed in fibroblast transformation by v-Rel. In addition, TCIO activates c-Jun N-terminal kinase (JNK) which phosphorylates and activates c-Jun. v-Rel may, therefore, regulate AP-1 activity not only at the transcriptional level, but also at the post-translational level through the TC1O activation pathway. The last aim of this proposal is to determine if TCIO plays a role in v-ReI-mediated transformation.